Press-fitted hub and camshaft

ABSTRACT

The invention relates to a hub ( 1 ) with a hub opening ( 2 ) in the front face ( 8 ), for press-fitting to a base body, whereby the hub ( 1 ) comprises a insertion region (A 2 ), tapering in the pressing direction, characterized in that a cylindrical section is arranged between the front face and insertion region (A 2 ), viewed in the pressing direction. Furthermore, a hub ( 1 ) with a tapering insertion region (A 2 ) is disclosed, whereby said insertion region (A 2 ) has a length of 40% to 96% of the total length (L) of the hub ( 1 ). The invention further relates to a camshaft with at least one cam ( 9 ), associated with said hub ( 1 ).

The present invention relates to a hub and a cam with a hub for pressingonto a base body and a camshaft with at least one pressed-on hub, inparticular, a cam.

It is known to make camshafts by pressing cams onto a shaft. On therespectively provided positions for the cam, the shaft is machined, suchthat a material aggregate exists, whose diameter exceeds that of theshaft. Upon pressing on, this material is deformed by the cam, so thatthe cam is fixed by a lateral pressing onto the shaft.

Cams for such a manufacturing method of camshafts are described indocuments EP-A2 1058033 and WO-A1 01/94802.

The hub opening of a hub or a cam according to document EP-A2 1058033 isdesignated by two conically formed sections of the hub. These two hubsections connect successively to the front face of the cam, forward inthe press-on direction. The two conical sections each have a differentincline. With this profile structure, the disadvantage exists in thatwith pressing on of the cam onto the shaft, already at the beginning ofthe cam opening, a force effect acts on the cam, and so tensioning inthe cam material can occur. This tensioning leads to microscopic tearsin the structure and can cause a weakening or collapse of the attachmentoperation, and likewise, can cause functional destruction of thecamshaft based on the deformation.

WO-A1 01/94802 shows a cam with an inlet area, which takes upapproximately half of the cam or hub width. The profile of this inletarea is described as conical and goes continuously over into a hubregion, which takes up the remaining width of the hub and is eitherconical or cylindrical. With this structure of the hub, a shifting ofthe connection tensioning in the center of the hub width should bepossible. However, it should be noted that already after the beginningof the inlet region, a deformation of the material aggregate on theshaft takes place. Therefore, in this region, damage of the materialconnection with the result of microscopic tears in the outer region ofthe cam hub with the previously described effects is to be expected.

The object of the present invention is to avoid the disadvantages of theknown hubs and to make an alternative hub for pressing onto a base body.

The object is solved by a hub for pressing onto a base body, whereby thehub has a hub opening, which is defined by hub front faces, and wherebythe hub has an insertion area A2 tapering in the press-on direction P,and the hub opening is characterized by a cylindrical section A1, whichis arranged between the front face and insertion area A2 as viewed inthe press-on direction.

With the term “hub” in the sense of the present invention, a sectionwith a through-going opening within a component is to be understood, forexample, those required with cams, wheels, cog wheels, eccentric rings,sensor rings, curved disks, or the like and for the mounting of cams,cogwheels, eccentric rings, sensor rings, curved disks onto a base body.Although the description relates substantially to hubs in cams, theinvention is not limited thereto. Cams can be formed as a separateelement, for example, tube-shaped. As a base body, also shafts, tubes,or also bearings (for example, ball bearings or bushings) can be used.Such cams are generally attached to or in the component, by which thehub is supported. Cams can be formed also integrally as an opening in acomponent.

A cylindrical embodiment of the section A1 of the hub avoids a directeffect of force between a component or a base body on which the hub isto be placed and the hub in the region of the front face, since thedeformation of the material aggregates on the shaft begins uponpressing-on of the hub on the base body first in the tapered insertionregion. Any connection strains occur, therefore, first in the insertionsection A2; they act on the fixed seat of the hub on the base body. Thebase body can be a shaft, which can comprise solid material as well as ahollowed-out tube, or the like.

By avoiding the connection strains in the cylindrical section A1, theformation of weak points, such as microscopic tears or deformations ormaterial distortions in the body, which supports the hub, for example,the running surfaces of a tire or a cam, are avoided. Damage to thefunction of the cam, as well to the material stability of the cam, isprevented.

Generally, the sequence of sections or areas of the hub are to beunderstood, in that, respectively, a lesser number lie forward in thepress-on direction. The press-on direction is that in which, forexample, the cam is guided over the base body. The cam front face is thesurface of the cam, whose normal is oriented parallel to the press-ondirection.

Advantageously, the hub of the present invention has a cylindricalsection A1 of the hub opening, whose diameter is at least the same sizeas the largest diameter of the base body. Such a diameter D1 permits asimple placing of the hub on the base body and makes possible uponpressing on, the avoidance of existing connection strains in the regionof the front face. A force effect between the base body and the hub inthe cylindrical section A1 is not formed.

Likewise advantageously, a hub is formed, which has a hub opening with asecond cylindrical section A3. This second cylindrical section A3 isarranged on the opposite side of the insertion area A2, with referenceto the first cylindrical section A1. This section A3 also avoids theformation of weak points upon pressing-on of the hub, in particular, onthe second front side of the hub, since the diameter of the base bodyalready is reduced in the insertion area or insertion section A2 to themass of the unmachined base body, in particular, the shaft. Nosubstantial force transmission between the shaft and the hub takes placein section A3.

Essentially, the diameter D1 of the first cylindrical section A1 isgreater than the diameter D2 of the cylindrical section A3.

One embodiment of the hub of the present invention is distinguished byan insertion section A2, which has a curved profile. This profilecorresponds to circular segments arranged on one another, whereby thesecirculate segments have different radii. The length as well as theradius of the individual circular segments are directed toward thedesired profiled structure. Of course, the profile also can be formed bysections of other curved shapes. The radii of the circular segments,which are adjacent to the first cylindrical section A1, are small.

The curve progression to the third section A3 is based on circularsegments with a respectively increasing and greater radius. Thecontinuous curvature of the curved profile permits an avoidance of amaximum connection strain and a force-fit connection extending over alarger area.

The curved segments cross over preferably continuously on another; thatis, they connect tangentially to one another, respectively. The curvedsegments, however, also can discontinuously cross over one another; thatis, on the respective transition points, a transition edge is provided.In addition, the first curved segment can continuously ordiscontinuously connect to the section A1.

The same is true for the last curved section, which can run continuouslyor discontinuously into the section A3. With a particularly simpleembodiment, the curve between the sections A1 and A3 are formed by aradius, which, for example, connects discontinuously with the formationof the transition edge E1 to the section A1, and for example,continuously, that is, without formation of a transition edge in thesection A3.

In a preferred embodiment, the insertion area (section) A2 of the hub isdivided into two subsections, which are formed along the longitudinalaxis of the hub in the form of a truncated cone. Therefore, bothtruncated cone-shaped subsections have different conical angles. Theconical angle K1 of the subsection A2′ adjacent to section A1 is greaterthan the conical angle K2 of the subsection A2″ adjacent to section A3.The different conical angle permits, on the one hand, an improvedcentering of the hub upon pressing onto the base body and, on the otherhand, a sufficient force-locking ability between the hub and the basebody. In particular, in view of the-frictional connection ability, it isimportant that this is provided over a sufficient longitudinal area ofthe hub, in order to permit a permanent connection also under operatingconditions. Preferably, in addition, the cone with the conical angle K1is opened in the same direction as the cone with the conical angle K2.Thus, a substantially continuous transition from a larger diameter to asmaller diameter can be assured. At the same time, the frictionalconnection between the hub and the base body is created over a widerregion.

As “conical angle”, the angle which is determined viewed from thefictional vertex of the truncated cone to the widening of the fictionalcone is intended. The half value of a conical angle, therefore, providesthe increase or incline of the conical surface with reference to theheight of the truncated cone. The spatial orientation of the truncatedcone to the hub is such that the truncated cone vertex coincides withthe longitudinal axis of the hub.

In a preferred embodiment, the insertion area A2 of the hub 1 is formedby an individual truncated cone (cone), which tapers originating fromthe diameter D1 to the diameter D2.

In this manner, the edges E1 and E2 are formed on the transition points.

In a further preferred embodiment, the cam has a diameter D1 in thefirst section A1, which is at least the same size at a diameter W1 ofthe base body. The diameter W1 corresponds with the diameter of thematerial aggregate existing on the base body from a machining of thebase body. These material aggregates are in the form of coils or bars.The material aggregates can extend either in the circumferentialdirection of the base body or parallel to the longitudinal axis of thehub. Based on the selection of the diameter D2 as at least the same sizeas the diameter W1, the hub can slide upon pressing-on first over thematerial aggregate, without material deformation. The hub is guidedopposite to the hub and makes possible an improved centering of the hubon the base body. At the same time, as previously described, also ashifting of possible connection strains takes place in the centralregion (insertion section A2) of the hub and a related avoidance of weakpoints on exposed points of the cam. As exposed points, the front faceor the region of the cam lying directly thereunder is to be understood.

Likewise, it is advantageous to form a hub, in which the diameter D2 isat least the same size or bigger than the diameter W2 of the base body.The diameter W2 corresponds with the diameter of the unmachined basebody. The suitable selection of the diameter D2 makes possible,likewise, a guiding of the hub onto the base body during pressing-on.

At the same time, the formation of substantial connection strains inthis second cylindrical section A is avoided, and therewith, likewise,the formation of weak points with possibly negative effects on thelongevity of the hub-base body-connection. The diameter D2 relative tothe diameter W2 is preferably selected, such that a clearance fitbetween the hub and base body is achieved.

In one embodiment, the hub of the present invention has a first sectionA2, which includes 2% to 30% of the entire length L of the hub. Withsuch a length, it is assured that, on the one hand, a sufficient guidingof the hub is achieved, and on the other hand, possible connectionstrains are removed far enough from the front face and exposed points ofthe hub, in order to avoid the initially disclosed disadvantageous.Preferably, the section A2 has a length of 5% to 15% of the entirelength of the hub.

It is likewise advantageous if the hub has a third section A3 with alength of 2% to 30% of the entire length L of the hub. Such a lengthensures that no substantial connection strains exist in the region ofthe section A3, which could lead to weak points on the exposed points.

Also, a sufficiently good centering of the hub on the base body is madepossible. Preferably, in addition, a length of the section A3 is from 5%to 15% of the entire length L of the hub.

In a further embodiment, the second insertion section A2 of the hubincludes a length of 40% to 96% of the entire length L of the hub. Thislength of the insertion area A2 forms the region of the hub, whichaccommodates the frictional connection of the hub and shaft. This isimportant, in order to ensure an adequate functioning of themanufactured camshaft also under conditions of long-term use.Preferably, the insertion section has a length between 70% and 90% ofthe entire length L of the hub.

A further aspect of the hub of the present invention is the longitudinalratio of the two subsections of the insertion section A2. The ratio ofthe subsection A2′ to the subsection A2″ lies between 0.1 and 10. Bymeans of a suitable selection, the development of the frictionalconnection between the hub and the base body is controlledadvantageously. Preferably, a longitudinal ratio between a firstsubsection and section subsection is from 0.1 to 5.

Furthermore, it is advantageous if the hub has a first conical angle K1of 10° to 40°. This conical angle region permits driving the materialdeformation up to the point that a frictional connection between the huband base body can be achieved directly.

A hub according to the present invention advantageously has a secondconical angle K2 between 1° and 15°. This conical angle range leads toan expanded contact area between the hub and the shaft, which creates anapproximately uniform frictional connection between the hub and basebody. Based on such a structure, a possible maximum of connectionstrains is substantially reduced or avoided, and therewith, non-uniformand damaging loads are reduced.

In a further embodiment, a hub of the present invention has at least onerecess, which extends at least over the length of the section A2 and A3of the hub. Under the term “recess”, a material demarcation, whichdefines a small part of the circumference of the hub and which extendsradially outward at a maximum to the diameter D2 originating from thelongitudinal axis of the hub, is to be understood. Such a recess, forexample, is viewed as a narrow channel parallel to the longitudinal axisof the hub, which continues in a small circumferential region of the hubfrom the first section A2 through the sections A2 and A3. Such a recessensures that additionally, from a frictional connection, a form fitbetween the hub and the base body is achieved, and thereby, a rotationof the cam in the circumferential direction is avoided.

The invention, in addition, includes a system having a base body, inparticular, a shaft, and a cam, whereby the hub penetrates the cam orits front faces. The hub has a tapered insertion area A2. The hub andshaft are formed, such that upon pressing-on of the cam, the distance ofthe point for a first contact between the largest outer diameter of theshaft and the insertion area A2 amounts to at least 2% to 40% of theentire length L of the hub.

Distance values of at least 3% to 20% are preferred, and furtherpreferred is at least 5% to 15% of the entire length L of the hub.

In addition, the present invention relates to a camshaft, on which atleast one of the previously described inventive hubs, in particular, acam, is pressed.

As the exemplary embodiment for a hub, in the following description ofthe invention, a cam for constructed camshafts is described. Theinvention, however, is not limited only to cams for constructedcamshafts. Hubs, for example, can be formed as cogwheels, eccentricrings, sensor rings, curved disks, or the like.

The schematic representations of the hub of the present invention show:

FIG. 1: a view of the pressing-on side of a cam.

FIG. 2: cross section Q-Q′ of the cam of FIG. 1.

FIG. 3: cam cross section and shaft with material aggregate beforepressing on.

FIG. 4: cam cross section and material aggregate of the shaft afterpressing on.

FIG. 5: further embodiment of the cam with an axial running recess.

FIG. 6: further embodiment of the insertion section A2 with an axiallyrunning recess.

FIG. 7: further embodiment of the insertion section A2.

FIG. 8: further embodiment of the insertion section A2.

The figures show embodiments of hubs and cams with the features of theinvention in a schematic representation; they do not represent exactproportions or dimensions and serve purely for clarification of theprinciple structure of a hub according to the present invention.

According to FIGS. 1 and 2, a cam 9 has a hub 1 with a hub opening 2 inthe front surface 8. The cylindrical section A1 with the diameter D1 isclosed off by the edge E1 (not recognizable in the figure). The firstsubsection A2′ of the second section (insertion area A2) connectsthereto. The surface of this subsection A2′ corresponds to a truncatedcone with the conical angle K1. This is recognizable in FIG. 2, whichshows a section along Q-Q′ of FIG. 1. The following subsection A2″likewise is formed to be a truncated cone, but has a smaller conicalangle K2, which is smaller than K1. Section A3 of the hub opening 2 hasa cylindrical shape with the diameter D2.

Likewise, the transition edges E1, E2, and E3 can be recognized, whichclarify the subdivision of the nub 1 into the individual sections A1,A2′, A2″, and A3.

Both FIGS. 3 and 4 show a base body 3 formed as a shaft withcorresponding material aggregates 5. The arrow P, therefore, shows thepressing-on direction of the hub opening 2. In FIG. 3, the cam 9 isdisplaced or pressed onto the based body 3 to such a point that thematerial aggregates 5 are located in section A1 of the hub opening.

It can be recognized clearly that still no material deformation hasoccurred. This is visible in FIG. 4, which shows the cam 9 afterpressing on. The material aggregates 5 lying behind in the pressing ondirection are located already in subsection A2″ of the hub opening 2 andhave already been substantially deformed (material deformation 6). Thesection A3 takes up the shaft ridges in section A2, without deformationof this additionally in section A3. The base body 3 has a diameter W2 inthe unmachined region and in the region of the material aggregates 5,has a diameter W1.

A recess 7 in the hub opening 2 of the hub 1 of the cam 9 is shown inFIG. 5. In the view of the front face 8, it can be seen how the recess 7extends only into a part of the radial circumference of the hub 1. Theradially most outward point of the recess 7 from the longitudinal axis 4coincides with the surface of section A1. Therefore, the recess 7 can bedesignated as a narrow channel, since it extends over the length A2 andA3. This recess 7 affects no material deformation upon pressing-on ofthe cam 9 onto a base body 3. Therefore, the cam 9 performs acircumferential-side fixing onto a base body 3. Also, more than onerecess 7 can be located in the hub 1. The profiling of such a recessalso can be adapted to the necessary specifications. FIG. 6 shows afurther embodiment of the section A2 of the hub 1. This section A2 hereis formed by a single cone, which connects sections A1 and A3 by theinterior edges E1 and E2. In FIG. 6, the recess 7 is shown in crosssection. In addition, also the half conical angle K1 for the section A2as well as the diameter D1 and D2 of sections A2 or A3 can berecognized.

A further embodiment of the section A2 of the hub 1 according to thepresent invention is shown in FIG. 7. In addition to the two sections A1and A3 of the hub opening 2, the cam 9 has a one-part section A2. Theprofile of the section comprises a continuously changing curveprogression. The curve progression can be described as a succession ofcircular segments, whereby the radius of these circular segmentsenlarges progressively. The circular segment connecting directly tosection A1 has the smallest radius of all of the circular segments,which form the curve progression, that is, the profile of section A2.

The largest radius, which opens directly into the section A3, canconnect by means of a transition edge E2 discontinuously, as shown inFIG. 7, to section A3. This transition in region A3, however, also cantake place continuously, that is, without formation of an edge E2. Inthis case, the largest radius of the section A2 runs tangentially in thesection A3 (analogous to FIG. 8). The curve progression in section A2also can be formed by a single radius R, which connects discontinuouslyto section A2 with formation of the edge E1 and opens tangentially, thatis, continuously, without edge E2 into the region A3.

Based on the increasingly flattened profile progression in section A2 inthe direction of section A3, the connection strains are distributed overa larger area, without causing excessively large load maximums. Theconnection strains, however, are simultaneously displaced into theinterior of the cam 9. Thus, structure defects, such as microscopictears in the outer regions A1 and A3 of the hub opening 2, are avoided.The functionality, in particular, the long-term stability, is thereforeimproved: in addition, it is conceivable that the curve profile isdivided into two or more subsections with respective individual curveprofiles, such as that described for the embodiment with truncatedcone-shaped sections.

An embodiment of the cam 9 of the present invention is based on a cambody made of ball bearing steel with a cam width of 15 mm. The length ofthe individual sections A1 and A3 as well as the insertion section A2 ofthe hub opening 2 amounts to 1 mm, 1 mm as well as 13 mm. The diameterD1 of the section A1 amounts to 25.6 mm, whereas the diameter D2 ofsection A3 amounts to 25.0 mm. The insertion section A2 is subdividedinto the subsections A2′ and A2″ with, respectively, lengths of 2 mm and11 mm. The subsection A2′ has a conical angle of 30°, and the subsectionA2″ has a conical angle of 15°. The rotating surface of the cam 9 aswell as the surface of the hub 1 is hardened, in order to reduce theoperating loads and to increase longevity.

With the making of a camshaft, on the corresponding points of the shaft(base body 3), a material aggregate 5 is produced by machining, whoselength corresponds approximately to the cam width, that is, 15 mm andits diameter difference W1 minus W2 amounts to approximately 0.6 mm. Acam 9 according to the present invention is placed on the shaft 3 andpressed with a pressing force of approximately 20,000 Newton over thismaterial aggregate.

In this manner, the correct pressing-on must be attended to, inparticular, in view of the positioning of the hub center, that is, ofthe insertion section A2 over this material aggregate. After completionof pressing on of the first cam 9, the further cams 9 are successivelypressed on with the correspondingly predetermined distance onto therespectively, individually produced material aggregates 5.

REFERENCE NUMERALS AND NOMENCLATURE

-   1 hub-   2 hub opening-   3 base body-   4 longitudinal axis of the nub-   5 material aggregate-   6 material transformation-   7 recess-   8 front face-   9 cam-   A1 longitudinal section 1-   A2 longitudinal section 2-   A2′ subsection of A2-   A2″ subsection of A2-   A3 longitudinal section 3-   D1 diameter 1-   D2 diameter 2-   E1 edge 1-   E2 edge 2-   E3 edge 3-   K1 conical angle 1-   K2 conical angle 2-   L hub width-   P press-on direction-   Q-Q′ section axis-   R arch, radius-   W1 diameter of material aggregate-   W2 diameter of base body

1. Hub (1) with a hub opening (2) in the front face (8) for pressingonto a base body (3), whereby the hub opening (2) has an insertion area(A2) tapering in the press-on direction, characterized in that in thepress-on device, a cylindrical section (A1) is arranged as viewedbetween the front face (8) and insertion area (A2).
 2. Hub (1) accordingto claim 1, characterized in that the diameter (D1) of the cylindricalsection (A1) of the hub opening (2) is at least the same size as thelargest diameter of the base body (3), on which the hub (1) is to bepressed.
 3. Hub (1) according to claim 1 or 2, characterized in that thehub opening (2) has a second cylindrical section (A3), whereby thesecond cylindrical section (A3) with reference to the first cylindricalsection (A1) is arranged on the opposite side of the insertion area(A2).
 4. Hub (1) according to one of claims 1 through 3, characterizedin that the tapered insertion area (A2) has a curve profile, whereby thecurve profile preferably is formed from circular segments with differentradii placed on one another, and whereby the radii of the circularsegments are smaller toward the cylindrical section (A1).
 5. Hub (1)according to one of claims 1 through 3, characterized in that theinsertion region (A2) has a curve profile, whereby the curve profilepreferably is formed by an arch (R), which discontinuously connects tothe cylindrical section (A1) and preferably opens discontinuously orcontinuously into the section (A3).
 6. Hub (1) according to one ofclaims 1 through 3, characterized in that the insertion area (A2) isformed by a truncated cone, which connects the sections (A1) and (A3) bymeans of transition edges (E1) and (E2).
 7. Hub (1) according to one ofclaims 1 through 3, characterized in that the insertion area (A2) isdivided into two subsections and both subsections are formed in theshape of a truncated cone along the longitudinal axis (4), and that thecone angle (K1) of the subsection (A2′) arranged toward section (A1) isgreater than the cone angle (K2) of the subsection (A2″) arranged towardsection (A3).
 8. Hub (1) according to one of claims 1 through 7,characterized in that the diameter (D2) is at least the same size as thediameter (W2) of the base body (2), whereby the diameter (W2)corresponds to the diameter of the unmachined base body (2).
 9. Hub (1)according to one of claims 1 through 8, characterized in that the lengthof the first cylindrical section (A1) is 2% to 30% of the entire length(L) of the hub (1).
 10. Hub (1) according to one of claims 1 through 9,characterized in that the length of the second cylindrical section (A3)is 2% to 30% of the entire length (L) of the hub (2).
 11. Hub (1)according to one of claims 1 through 10, characterized in that thelength of the insertion area (A2) includes 40% to 96% of the entirelength (L) of the hub (2).
 12. Hub (1) according to one of claims 7through 11, characterized in that the ratio of length of the subsection(A2′) to the subsection (A2″) lies between 0.1 and
 10. 13. Hub (1)according to one of claims 7 through 12, characterized in that the firstconical angle (K1) is 10° to 30°.
 14. Hub (1) according to one of claims7 through 13, characterized in that the second conical angle (K2) is 1°to 15°.
 15. Hub (1) according to one of claims 1 through 14,characterized in that the hub (1) contains at least one recess (7)extending over the entire length (L) of the hub (4), whereby the recess(7) defines a part of the periphery of the hub opening (2) and therecess (7) extends radially outward at a maximum to the diameter (D1).16. Cam (9) with a hub (1) according to one of claims 1 through
 14. 17.Camshaft including at least one cam (9) according to claim 16 and a basebody (3), in particular, a shaft, on which at least one cam (9) ispressed on.
 18. System including a base body (3), in particular, ashaft, and a cam (9), whereby the cam (9) has a hub (1) in the frontface (8) for pressing onto the base body (3), and whereby the hub (1)has a tapered insertion area (A2), characterized in that upon pressingon of the cam (9), the distance of the point for a first contact betweenthe greatest outer diameter of the base body (3) and the insertion area(A2) is arranged at least 2% to 30%, preferably at least 3% to 20%, andfurther preferably, at least 5% to 15%, of the entire length (L) of thehub (1) from the front face (8).
 19. Camshaft, including at least onecam (9), whereby the cam (9) has a hub (1) with a hub opening (2) forreceiving a base body (3) formed as a shaft, whereby the hub opening (2)has an insertion area (A2) tapered in the press-on direction,characterized in that, viewed in the press-on direction, a cylindricalsection (A1) is arranged between the front face (8) and the insertionregion (A2).